Processing speed, as measured by the Sternberg Memory Scanning
Test, was significantly correlated with posterior fossa lesion volume and
slowed reaction time in seven out of eight patients (six out of seven with
SPMS) with any lesion volume in the posterior fossa suggesting a 'threshold
effect'.

Processing capacity as measured by the Salthouse Keeping Track
Test was not significantly correlated with the MRI measures.

Cognitive
performance did not correlate with Expanded Disability Status Scale score,
depression or fatigue, and patients performed within normal limits on tests
of attention/concentration ability.

The significant relationship between
posterior fossa lesion volume and memory scanning speed in this study suggests
that pathological damage in the posterior fossa may contribute to slowed
cognitive processing and may be an important direction for future studies
of cognitive function in multiple sclerosis.

Lack of correlation of cognitive
measures with the other MRI measures may be due to low lesion volume relative
to other studies, sample composition, and limited pathological specificity
of the MRI measures.